tracing: Improve "if" macro code generation

With CONFIG_PROFILE_ALL_BRANCHES=y, the "if" macro converts the
conditional to an array index.  This can cause GCC to create horrible
code.  When there are nested ifs, the generated code uses register
values to encode branching decisions.

Make it easier for GCC to optimize by keeping the conditional as a
conditional rather than converting it to an integer.  This shrinks the
generated code quite a bit, and also makes the code sane enough for
objtool to understand.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: brgerst@gmail.com
Cc: catalin.marinas@arm.com
Cc: dvlasenk@redhat.com
Cc: dvyukov@google.com
Cc: hpa@zytor.com
Cc: james.morse@arm.com
Cc: julien.thierry@arm.com
Cc: luto@amacapital.net
Cc: luto@kernel.org
Cc: rostedt@goodmis.org
Cc: valentin.schneider@arm.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190307174802.46fmpysxyo35hh43@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 445348facea97d2755f371198ca5730302c3f1ba..d58aa0db05f9438cbe3639a7d47788b6acdd4f33 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
                                .line = __LINE__,                       \
                        };                                              \
                ______r = !!(cond);                                     \
-               ______f.miss_hit[______r]++;                                    \
+               ______r ? ______f.miss_hit[1]++ : ______f.miss_hit[0]++;\
                ______r;                                                \
        }))
 #endif /* CONFIG_PROFILE_ALL_BRANCHES */